The present invention relates to an actuating device for the presser foot of a sewing machine.
A known actuating device for a presser foot is disclosed in DE 36 04 299 C2 (corresponding to U.S. Pat. No. 4,658,752). A sewing machine is disclosed which has a presser foot drive in the form of a double-acting pneumatically operated piston-cylinder drive. In more detail, the piston rod of the piston-cylinder drive is directly connected to the presser bar, and the cylinder and the piston are connected with the piston bar aligned with the presser foot bar. Within the cylinder, a prestressed compression spring presses the piston and thus presses the presser foot bar together with a presser foot arranged thereon against sewing material which is present on the base plate of the sewing machine. Upon corresponding action of compressed air on the piston-cylinder drive, the presser foot is raised against the force of the spring. The force of the spring is predetermined by its design.
One disadvantage of the known presser foot device is that particular care is needed with respect to its design in order, on the one hand, to arrange it exactly in alignment with the second bearing which guides the presser foot bar and, on the other hand, to assure a continuous sealing of the presser foot bar from the pressure chamber of the pneumatic cylinder. Beyond this, no information can be obtained from the literature as to how the actuating device which is developed in the form of the pneumatic cylinder is to be developed with respect to proper manufacture and assembly.
This presser foot has the further disadvantage that the operator cannot adjust the force applied by the spring as well as the stroke length by which the presser foot can be lifted off the material being sewn, in accordance with the requirements of the specific operation for the production of a seam.
Federal Republic of Germany Utility Model 81 23 748 discloses a presser foot device of a sewing machine in which the spring force acting on the presser foot bar and the position of the presser foot in its lower position can be adjusted by set screws. The presser foot device has an actuating device provided with a pneumatic cylinder which is assembled from a considerable number of structural parts.
Pneumatic cylinders with hollow piston rods are shown on a page from the Pneumatic Cylinder Catalog (Pneumatic Main Catalog), 22nd Edition, page 1.211-3, FESTO Pneumatic Esslingen.
DE 39 07 240 A1 shows an actuating device for the presser foot of a sewing machine, in which a presser foot is articulated on a lever which extends substantially horizontally and is swingable around the horizontal, and in which this lever can be actuated by a piston-cylinder drive. This piston-cylinder drive can act in any direction whatsoever; it is merely necessary to assure that a torque is still produced around the swivel axis of the lever. This known actuating device does not correspond to the actuating device of the type involved herein. The problems occurring in the actuating device of the type concerned herein also do not occur with the actuating device of the reference, and the features proposed in accordance with the present invention are also not known from the reference.